Draft control



Sept. 30, 1952 O. E. WADENSTEIN DRAFT CONTROL Filed June 3, 1949 ama- QMm- W Patented Sept. 30, 1952 DRAFT CONTROL 7 Oscar E.'Wadenstein, St.Paul, Minn., assig nor,

" by-mesne-assignments, toFueLReduction Engineers; Inc., St. Paul,Minn., a corporation, of

Minnesota.

PATENT OFFICE App1ication June-3, 1949, Serial No. 97,018:

be" maintained by more or less closing the by-pass damperin thebr'eeching tdinci'ease over-fire draft or by opening" th'edamper' to a'greater or lesser extent to decrease over-fire'diaft by by-' passingstack suction". However; the common types off motor'ized by-pass'dam'pers described above ar'e limited toa single rate'of overfire draftdependent upon the' setting 'of the staticpressure regulatorin iisei f It I have fiound that boilers or furnaces'will-operate niore'economically if over-fire draft is variedto su'ppl'y more or lessdraft'as the'volume of; fuel'and air is increased or decreased. Thus inmy variable'air new control I p'rovide lip to three staticpressureregulators with each regulator adifisted to pro'vide adifl'erent fixed rate of over-fire draft "depending "upon therequirementsof the are; I

rates' or draft; for'example .i2-;draft by {Water for a peak boilerload, .08"' for a half load and .04 for a quarter mad.) Two static'pressure regulat'o'rs' will provide two" 'rates of over-fire draft.contr 'i's switched from one static pressure regulator toth'e otherbyelectricity, the over-fire draft will modulate oF'varybetween the fixedsettingsof' the regulators consequentl modulatin'g'dr'aft is also aparrot the rese t inventioil." V L An added featureof'the presentinvention lies the provision of a'mansfor controlling overfiie'draftatiowestd'esirame rates or draft. I

have-demonstratedthat the combustion 'efiiciency or a'ilie,whether-coated, or gas, can be maid tamed at a high point of fiicie'ncywhen over-fire draftis decreased as fuel and blower air'ratiosaredecreasem 1 I These and? other objects and novel features of my.inv'eritioniwill be rirore clearly and fullyset forth in the'followingspecificatioh and claims.

. 8 Claims, (Cl.'236- 15 I reestau pressure regulators, each acti Viifidseparately byelectricity; WiH'pIDVide three Inthe drawingsforming apartof my specification: Figure-1 is a diagrammatic perspective view showingafurnace to which, my control has been applied.-

hem f I v s. The control system is used in coniunction with a furnaceorboiler 10 which may-burn any desired type of fuel. In the furnaceillustrated: an oil burner l l is employed. -The oilburner is providedwith a blower ['2 to supply primary forced air, and a damperedopening-into the furnace below the oil burner to supply secondary air bystack suction. The furnace I0 is connected to f the breeching l3whichconnects the furnace with the chimney stack 14. I

'The oil burner II is supplied with oil from-an oil supply lineindicated at 51; which passes through a control valve 2. A lever 3controls the valve 2 and also an electric control such as. a-

multi-position switch or a rheostat 4. Pivotal movement of the lever 3simultaneously increases or reduces the oil supply and the air supplyprovided by the blower I2. The rheostat' l is connected to the blower I2by an electric conduiti.

The lever 4. is connected by a'chain or other.

linking meanst to the switch which'will-be" later described in detail. Ameans is provided foractuating the lever 4, such as "the pressureactuated apparatus. 1 'connectedtothe leverg4 by a 1mm; When thepressure actuated device I indicates a needfor-increased fueland. airfeed the lever 4' is oscillated upwardly: When the necessary pressure isbuilt up in the device [the lever I is swung downwardly to decrease thefuel and air supply. The'switch 35 is "connected tothe re-' mainder 'ofthe system by azconduit'9. This'sys-t,

tem is onJy'illuStr'ative of manywhich could "be used. f

obv'iously the oilburner is optional, and gas 'or' coalcan also be used.The gas maybe suppliedin the usual manner and ablowersuch as I 2 mayv beused in conjunction therewith to'supply' a forced draft of air.Similarly :the *furnace or- .boiler l0 may comprise a 'coalburningapparatus supplied with coal by a suitable .stoker or "similar device. Ablower such as ['2' is alsousedin con:

junction with this type of furnaceor boiler. The

breeching I3 is provided with aby-pass-passage l5 provided withadamperiG-at its'outer extremity. The position of the damper I6 iscontrolled bymeans of a jdampercontrol motor 11.- The motor I! mayoperate ineitherdirection to open or close the damper I 6, v;

Figure 2 is a diagram of the wiring ofmy sysone terminal of a triplethrow switch 35.

fi V '1- ff; 2,612,319

A static pipe I 9 extends into the furnace above tial to provide a lowdraft rate, while the regulator 20 is set to maintain a relatively highstatic pressure differential, to provide a high rate of draft. With theuse of a third static pressure regulator 2| a medium rate ofover-fire'draft can be provided. Over-fire draft will modulate up ordown as electric current activates the various. static pressureregulators, one at a time.

With reference to Figure 2 of the drawings, it will be noted that twoterminals 22 and 23 and the first static regulatorl 8 are connected byconductors 24 and 25 to terminals 26 and 21 of the damper motor 'I.'Terminals 29 and 30 of the second static pressure regulator 20 areprovided with conductors 3| and 32 which are electrically cdnne'ctedtothe conductor 24'and 25 respectively. A thirdterminal 33 of the firstpressure regulator |8"is connected by a conductor34 to The thirdterminal 36 of the pressure regulator 20 is connected'by a conductor 31to the opposite pole of thetriple-throw switch 35. A third terminal39"o'n the damper'motor I is connected by a conductor to a line wire 4|or a suitable source of current of the desired voltage. The terminals 42and 43 of the triple throw switch 35 may be alternatel'y'connected tothe other line wire 44, providing asuitable source of supply ofelectrical current.

Where a third static pressure regulator 2| is empleyei the terminals 45and 46- thereof are connected by conductors 41 and 49 to the conductors'3| and 32, and consequently the conduc-' tors 24 and 25, respectively.In other words, the

three-static pressure regulators I8, 20, and 2| are wire" 4| is acommonwire to the motor and forms one side of the circuit tothe motorregardless of the direction ofrotati'on thereof. The conductors 24 'and'25 and" the extended conductors 3| and 321; and 4T, 49' connectedvthereto, respectively, form the remaining two sides of the circuits'tothe m'o'tor 1'. When the conductor 24 and its 'extensions 3| and 41 arein circuit, the motor I! will operate in'one direction to open thedamper.

When the conductor 25 and its extensions 32 and 49;are in circuit-themotor I! will operate 'inthe opposite directinn to close the connecteddamper. The switch 35 is controlled. by some portion of the operatingmechanism which is actuated si-f multaneously 'with any change of thefuel and air feed; "The switch 35 acts to'connect the line wirej 44.tothe conductor 34 through the switch terminal"42 when the boileris beingsupplied with fuel andairat azmin'imum rate, Thus during the periods' ofrelatively slow fuel feeding operation (as for-"example, one-quarterload), the static pressure regulatorl8is electrically connected in thecircuit? andvariations in "pressure above the fire bed will act'toconnect either the conductor 24 or the conductor 25into the circuit andthus to move the damper motor I! in one direction or the other. When theterminal 33 of the pressure regulator I8 i connected to the terminal 22,a circuit is closed through the conductor '24 so as to operate thedamper motor I! to open the connected damper Hi. When the'terminal33 isconnected to the third terminal 23, the circuit is closed from theconductor 34 to conductor 25. thus closing the circuit to the dampermotor IT to operate this motor in a direction to close the connecteddamper l8.

The pressure regulator is not specifically illustrated in detail in thedrawings, a this device is known in the art. The regulator acts tomaintain a fixed static pressure above the fire bed by opening orclosing the by-pass damper to a greater or lesser extent. For example ifthe differential static pressure desired to be maintained by theregulator I8 is .04 inch of water, a switch contact will connectterminals-33 and 23, when thepressure decreases below this amount. As aresult the damper 6 will beclosed until the pressure above the'fire bedagain becomes .04 inch of water. When the static differential pressureabove theflre bed increases above .04 inch, a contact will be formedbetween terminals 33 and 22, thus rotating the damper motor to partiallyopen the damper l6 until the pressure above the fire bed again becomes.04 inch. 7

.The static pressure regulator 20 acts in a similar manner whenthefumaceis feeding fuel at a maximum rate; When the fuel feedingapparatus is actuated to feed the furnace or boiler'at full speed, theregulator 20 comes into action, and the damper setting of thedamper I6is controlled by this regulator 20, As a result, thedraftv will bemaintained at ahigher level during these feeding operations. i p

When the switch 35 shifts control ofithe damper motor from one pressure--control--to. another,.a gradual change in differential pres-. sure isexperienced within the furnace-or boiler. For example, as the controlshifts from the regulator l8 to the regulator 20, the static pressuredifferential must be increased due to the higher. setting of theregulator 20. The by-pass' damper "5 will therefore close to a greaterextent until the static pressure called for by the-regulator-20 isreached. Any increase of staticpressure over the desired amountresultsin a closing of thecircuit to open the damper l6 somewhat. Contactbetween the terminals 36 and 29 actuates the motor H to open the damperI5, while contactbetween terminals 36 and 30 actuates the motor to closethe damper 6. Wherea third pressure regulator 2| is employed tomaintain; an intermediate static pres.- sure differential, as forexample .08 inch of water, this regulator is cut into the circuit by theswitch 35 when the fuel feed mechanism is feedingfuel at an intermediaterate; as for example, half speed. 1 Whenthe regulator 2| is incircuih'-it acts in the manner described to maintain the desired static pressuredifferential.

If the pressure differential i excessive when the regulator 2| is placedin the circuit (as would bethe case when the fuel .and air feed to thefurnace is reduced), the terminals 50 and 45 will be connected and a"circuit will be formed through conductors 41, 3| "and 24, opening the.damper until the draft is reduced to the desiredzextent;

' Any reduction of draft below .this will act to con- Similarly,- if thepressure: differentialfs too little when the regulator 21 i's' placed'inithe circuit fas would b'ethe case "when the fuel and'air feed to thefuma'ce is increased from' 'a. lower speed) the regulator-will tend toclose-the damper until the properly increased static pressuredifferential'is reached.

The triple throw control 1 the fuel -1'eedinechanism in anydesired'manner; If'the furnace orboileris provided' with-controls too'perate the-fuel and air feedatthree set speeds, the switch 35 maybecontrolled thereby-to cut a corresponding regulator into controllingposition. If the fuel feed fluctuates 'or modulates gradually from onefeed range to anothem the feed 'range'm'a y be divided into suita blesmaller rangesxeach' of Y which. may haveits'respectiveregulatory; 1 l'I' have found that myfsystem operates with particulareffectiveness-in,- conjunction with a system including an air by-passandlay-pass damper in-the breechingor stackr With this type ct-system"thepressure ab'ove the fuel bed is: controlledbyallowing more orless air to enter the'stack or breeching. As the by-pass damper opens, agreater'amount of air enters the stack or breeching and the draft actingupon thefire bed is-decreased. In other words, the suction effect uponthe fire bed decreases and' accordingly the'pressureat thispo'intincreases, decreasing the static pressure differential. Converselyas the by-pass damper moves toward closed position less air isallowedtoenter the by-passso that a greater draft or suction effect is created towork upon the fire bed.-- As a result the pressure above the fuel beddecreases as the by-pass damper closes, and the static pressuredifferential increases. V I

This type of control functionsmore effectively than a control in whichan internal damper is located in the breeching, stack, or boilerup-take. As-such an internal damper moves toward closed position the airpassing the damper merely tends to move at a higher velocity-5 Thus thedamper does not greatly change the static pressure-above the fuel beduntil the damper nears closed position in many installations. Thus themaximum control is provided at a time when the internal damper is almostclosed. Where the stack is high and there is substantial draft actingagainst a practically closed internal damper, boiler vibration orpulsation is severe. This fact combined with the fact that such a damperis subjected to high temperatures and may be injured thereby tends tocause my system to operate more effectively in conjunction with aIby-pass system employin a bypass damper.

It will be noted that during the peak operation of my furnace or boilerI maintain a fixed rate of draft over the grate level which has beenfound proper to produce good combustion. If the same rate of draft weremaintained above the grate level during the low operation period ofthe'boiler, poor combustion efficiency would result because of air dueto excess draft. However, by decreasing the over-fire draft on lowoperation as fuel feed is decreased, greater combustion efficiency willresult, because desirable fuel and air ratios are maintained andtemperature loss is minimized.

In accordance with the patent statutes, I have 7 described theprinciples of construction and operation of my draft control and while Ihave endeavored to set forth the best embodiment thereof, I desire tohave it understood that ohswitch may :be connected for v made.within-the: scope- 9! the vicuse'change'szmay e the following claimswithout departln zzfrom spirit of my invention. i v 'I'claimi:

1.;A. damper-co trol for use in eonjunctionwith a furnace having agasandsmoke outlet,- a hypass into said outlet, a by-passdamperin saidbi -pass, and, a fuel feeding mechanism which may-operate at full or.low speed intermittently; a first static pressure regulator formaintaining an above fire rate of draft of one relatively high value, asecond static pressure regulator for maintaining: an above fire-rate of'draft-ofiasec-. ond relatively low value, .a damper opera-ting means,and means connecting each of saidpres sure regulators selectively tosaid damperoperats. ing" means, and means controlled" by th intermittent operation ofzsaid fuel feedin meang forconnected to said damperoperatingmeansi 3. The structure described in claim =1 in-' which thepressure regulator operates upon' an increase of draft to opensaidby-pass damper' 'and op erates upon a decrease in pressure above thefire to close the by-pass damper. f v

' 4. A variable air flow control foruse inconjunction with'a furnaceprovide diwitha stack through which gas and smoke may flow, a by passfor' by passing air intothe gasan'd-smoke, a damper for regulating" theby-pass of air through said by-pass, and a fuel feeding mechanismoperable at various fuel feedin rates, the control including a staticpressure regulating means, said regulating means including aplurality ofelements each operable to' ma'intain a predetermined static pressuredifferential'above the grate level of the furnace, a damper motorconnected to said damper for actuating the same, means connecting saidelements with said damper motor for actuating said motor to maintain anyof the predetermined static pressure, differentials, and selectin meanssensitive to variations in fuel feeding rates for selecting an elementof said plurality of elements so as to maintain the desired pressuredifferential, said selecting means acting to select a greater pressuredifferential upon an increase in fuel feeding rate.

5. A variable air flow control for use in conjunction with a furnaceprovided with a stack, a connection between the stack and the furnace, adamper controlling the flow through said connection, and fuel feedingmechanism operable at a plurality of fuel feeding rates, the controlincluding a first static pressure regulating means capable ofmaintaining a relatively high overfire rate of draft, a second staticpressure regulator capable of maintaining a relatively low above-firerate of draft, each of said static pressure regulators being connectedto the furnace and sensitive to changing conditions within the furnace,a member associated with said fuel feeding mechanism and sensitive tovariations in fuel feeding I rates, means for actuating the damper toopen or close the same, means connecting each of said static pressureregulators to said damper actuating means to control the bperationthereof, a" selector in said connecting me'ansfor'selectively connectingeither ofsaid static pressure regulators to said damper actuating means,and means connecting said member sensitive to variations in fuel feedingrate to said selector and operable to select said first pressureregulator when said fuel feeding mechanism operates at a relatively highspeed, and selecting said second pressure regulator when said fuelfeeding mechanism is operated at a relatively lower rate.

' 6. A damper controlfor use in conjunction with a furnace having a gasand smoke outlet, a bypass into said outlet, a by-pass damper -.in saidby-pass; and a'fuel feeding mechanism which may operateat a relativelyhigh speed or a relatively lowerspeed, said control including a firststatic pressure regulator capable of maintaining an above-fire rate ofdraft of a relatively high value, a second static pressure regulatorcapable of, maintaining anabove-fire rate of draft of a secondrelatively lowvalue, a damper motor, a circuit tothedamper, motorincluding a switch actuated by variations in static pressure in saidfirst static pressure regulator, a second circuit to saiddampermotor'including switch means controlled by variations in static pressureinv said second static pressure regulator, and means selectivelyconnecting. either of said circuits to said damper motor,-and meansactuated by variations in fuel feeding rate of said fuel feedingmechanism connected to said selector for actuatin the same, said lastnamed means actuating said selector for selecting the first pressureregulator when said fuel feeding mechanism operate at a relatively-highspeed and selecting said second pressure regulator when said fuelfeeding mechanism operates at a relatively lower speed.

7'. The structure described in claim 6 and including a third staticpressure regulator capable of maintaining an above-fire rate of draft ofan intermediate value, and a third circuit to said dampermotor includingswitch means actuated by variations in static pressure in said thirdregulator, said selector being capable of selecting said 8 third circuitwhensaid fuel feeding mechanism actuates at an intermediate rate." r v'8. A' damper control for use in conjunction with a. furnacewhavinga gasand smoke outlet, a by-'-pass-into said'outlet, a by-pass damper in saidby-pass, and a fuel feeding mechanism which may operate at two differentrates of rfuel feed, the control including a first static pressureregulator formaintaining a relatively high above-fire rate of draft, asecond static pressure regulator capable of maintaining a relatively lowover-fire rate of draft, a damper operating motor, a first circuit:to'said damper motor including a switch actuated by variations in staticpressure in said first regulator; and said circuit also including aselector switch, a second circuit to said damper motor including aswitch sensitive-to variations in static pressure in said secondregulator, and also including said selector switch, said selector switchbeing capable of connecting either of said-circuits to a source ofcurrent, and means sensitive to variations in fuel feeding rateconnected to said selector switch for actuatingthe same to select thecircuit including said first pressureregulator when said fuelfeedingmechanism operates at a relatively high 'rate and selecting said secondpressure regulator when said fuel feedin mechanism operates at a rela'-'tively low rate.

OSCAR E. WADENSTEIN."

REFERENCES CITED The following references are of record in the file ofthis patent:

Adams Mar. 10, 1942

